Natural Light, Energy Efficiency

By Ellen Kollie

December 1st, 2009

Natural light has become an important part of facility design at all levels of education. The downside is that, during winter, building openings are a significant cause of heat loss and, during summer, they are a significant cause of heat gain. Add to that the myriad manufacturers plying their door and window wares, along with such confusing terms as R-value and U-value, and it can be quite challenging to know which end of a door or window is up.

Here, a handful of designers and suppliers offer their combined knowledge and experience so that designers and administrators can better know what to consider when making decisions about which doors and windows to use in their new building or renovation projects in order to get the most light and least heat loss/heat gain.

Consider This
“When you’re looking at your exterior fenestration,” says Christopher Chivetta, PE, LEED-AP, president of St. Louis-based Hastings & Chivetta Architects, Inc., “including windows and doors, be cognizant of how much natural light you’re bringing in, but also the ratio of window and door area to solid fenestration there is. It’s important to balance that ratio in order to provide ample natural light and a good thermal barrier for energy conservation.” He notes that, in recent years, the use of high-efficiency glazing systems has helped in energy loss and heat gain, but it is still the most energy-intensive portion of a building.

Dovetailing with the ratio of window and door area to solid fenestration is the building orientation. If you’re working on new construction and are able, site the facility facing south. “Typically, you can control the light better on the south elevation than on the east and west,” says Gary Jelin, AIA, vice president at TMP Architecture in Bloomfield Hills, Mich., “because the sun angles tend to be low on the east and west, particularly in the winter, and it’s harder to control light.”

Jelin also says to consider controlling light before it gets into the building. “In northern climates, the heat gain in summer has a bigger impact on air conditioning energy costs than heat loss in winter has on heating energy costs,” he notes.

Similarly, Jelin notes that technology has helped get more glass into buildings without as much heat loss in winter. Consider choosing high-performance glass which, he says, is more environmentally friendly these days than ever before — even performing better than the walls of your house — thanks to the insulation and gases used between panes.
Remember This
The experts noted a handful of door and window items of which designers and administrators sometimes need to be reminded. For example, that both need to be maintained for the life of the building, and the amount and kind of maintenance required should be considered in the early planning stages to rule out some products.

Specifically, for windows, it’s how often they have to be cleaned, how difficult it is to clean them and the special sealants required for preventive and deferred maintenance. For example, does the height and placement of the windows require a Genie lift for cleaning, or will a pole and squeegee from the ground do the trick? How many horizontal reveals are there? Will your staff be cleaning them, or will you hire someone, which will cost more?

For doors, it’s important to have high-quality weather seals and vestibules associated with them to avoid air infiltration. It’s also important to have the correct hardware, such as continuous hinges on main doors, for longevity.

Chivetta notes that it’s easy enough to forget the maintenance component of doors and windows during renovation or new construction simply because it’s so easy to get caught up in the cutting edge of new products and the excitement of the moment. Still, he reminds building owners to have this conversation early in the design phase, asking a lot of questions, and even involving the custodial and maintenance personnel.

Another item that is sometimes forgotten when specifying doors and windows is sound ratings. “A garbage truck or a siren outside can be distracting to students studying inside,” reminds Ebrahim Nana, president of NanaWall Systems Inc., Mill Valley, Calif., a provider of operable glass walls.

Finally, remember to consider natural ventilation and the opportunity to reduce the workload of the mechanical systems on good weather days. Steve Gille, education marketing manager for Wausau Window and Wall Systems, Wausau, Wis., which engineers window and wall systems for schools and other buildings, sometimes sees such a focus on mechanical systems and LEED certification during the design phase of new building projects that operable windows are altogether forgotten.
Know This
There are two things that the experts specifically want to educate building owners about when it comes to doors and windows.

The first is that they’re really a complex assembly of various building components coming together to create the exterior façade. “For instance,” says Chivetta, “there’s a close coordination between the masonry contractor and the window manufacturer. It’s not just one manufacturer supplying one component; it’s numerous manufacturers supplying numerous components, such as metal framing and caulk. There’s complexity and various parties involved.”

To this end, Chivetta recommends avoiding hybrid window systems and asking your designer to recommend something tried and true. Ask where has the window been installed, for how long and what the warranty is on each component.

The second thing the experts specifically want building owners to know is that, when it comes to windows, there are different classifications. “There is a commercial window versus a heavy commercial window versus an architectural window,” says Gille. “They’re not all on same playing field, and it all comes down to performance and longevity.”

Gille recommends that building owners rely on their designers to educate them. He also recommends inviting the manufacturers in to talk about specifications and warranties. Involve the custodial staff. Learn about what you’re getting versus what you’re not getting, he says candidly.

Think About This
Here are three things that the designers and suppliers would like you to think about the doors and windows you choose for your next building or renovation project.

First, think about air infiltration. “One of the things that amazes me is the sole focus on U-value,” says Nana, “which is the rate of heat loss of a window or door, and not combining that with air infiltration. In my mind, as a supplier, the two should be combined.” He points out that there’s no point using triple glazing and having the lowest U-value on a window if that window is drafty, but that it is the two combined that provides the greatest comfort.

Second, think about the fact that doors and windows are complex systems and there are new products coming out that can be beneficial in the long run. With that in mind, you have to decide if you want to be at the head of the pack in choosing a new product that probably costs more or be in the proven pack in choosing a product that costs a little less.

Third, think about the fact that there’s no excuse for poorly designed door and window systems, thanks to energy modeling. It allows you to predict operational costs, heat gain and heat loss simply by changing the amount and type of glass. An added benefit is that energy modeling allows the building owner to be a partner with the designer: “The owner gets excited about design,” says Jelin, “and is really able to make a contribution.”

Armed with some knowledge — not in the least technical — building owners can achieve the goal of letting natural light in to their educational facilities while keeping heat gain and heat loss to a minimum, thus getting the best of both worlds.